I'm trying to power a classic Nano and the PCA9685 servo controller below from a battery. I have a 7.2v LiPo and a 9.6v NiMH that can provide enough current- 340mA is the stall current of my servos, and only around 250 for typical operation, times 8 (I'm running 8 servos) plus a peak of 280mA for the Nano gets me to 3A at 5v exactly. Either of my batteries can comfortably discharge higher than 3a continuously.
I think either of those should be fine to wire to the VIN pin on the Nano, max voltage 12v.
It says its a 5v board, but it's a clone of this board:
This adafruit page says " If you have to, you can go higher to 12VDC, but if you mess up and connect VCC to V+ you could damage your board!" but I can't find that info in any datasheet for this board or its many clones. Is that real? I'm happy to buy the adafruit board if it can actually handle up to 12v.
Can I just wire both boards in parallel to the battery?
Servo V+ is independent, the chip only supplies the PWM signal.
If your servos can handle the battery voltage, use it for V+, and as warned, don't let it be Vcc 5 vo,ts for your Arduino power or for Vcc on the module.
The UBEC will work OK, it is a special,purpose version of a buck regulator, nothing but a buck regulator with convenient (or not!) connectors attached.
You can browse naked buck regulators at pololu.com.
Be sure to measure and confirm the regulator whichever you use. Specs tend to be aspirational, the only proof is seeing it work.
I test regulators with a dummy load, but it has never happened that it was a Good Idea, I've never had a failure that would have damaged anything attached. Just me being ultra conservative.
Oh, you can use the battery voltage in as many places as you want, just don't use it where 5 volts is the expected input voltage.
Obvsly you will have a common ground for the battery, the boards and the regulator.
Note the thick trace for V+ on the servo board, pick your wire gauge to handle the max current.
Just one thought, if you are using a buck regulator or the UBEC, that should be where you get the 5 volts for everything that can use it directly.
The Adafruit text seems clear - that module's logic wants 5 volts Vcc, and (but) its power section can handle 12 volts V+.
Using the UBEC 5 volts eliminates any waste from the Arduino on board regulator, which would be worse if you used the 5 volt out on that to power the servo board.
And it gives a degree of separation between the battery power line, which might have some trash on it from running the servos. A solvable problem, and steps should be taken to clean up the battery power lines, but the UBEC will make nice 5 volts for you.
And I will say that Lipos are an amazing source of power. I use them one cell plus a boost regulator, or batteries of two and more with a buck regulator.